This invention relates to an integrated thermal management and coolant system for an aircraft, particularly an aircraft having a turbo fan propulsion engine.
Modem sophisticated aircraft require equally sophisticated systems for thermal management and cooling. In typical modes of operation of the aircraft, lubricating oil for the engine and hydraulic fluid used in the various hydraulic systems as well as the aircraft mounted accessory drive (AMAD) require cooling. At the same time, the avionic systems of the aircraft will require cooling during operation, some by a liquid coolant and others by cool air. Concurrently, at low altitude or on the ground or at other relatively high temperature operating environments, the aircraft cabin requires cooling while at relatively low temperature altitudes such as at cruise altitude for a jet aircraft, the cabin will require warming. Through all of this it is generally desirable to heat the fuel delivered to the main propulsion engines to maximize the efficiency of the engines.
A common thread in many prior art systems is the use of the air in which the aircraft is traveling as a sink into which heat is rejected. Most typically, this air is both so-called xe2x80x9cram airxe2x80x9d and xe2x80x9cbleed airxe2x80x9d. Ram air is, of course, air that is literally rammed into an inlet on the aircraft as a result of the aircraft""s forward velocity through a body of air. A penalty paid for the use of ram air is the aerodynamic drag imposed on the aircraft as a result of the presence of one or more ram inlets.
In addition, the installation of ram air circuits in an aircraft so as to convey the ram air to a point of use is difficult. Moreover, in the case of aircraft intended for military use, ram air inlets all too often may provide an undesirable aircraft position indicating radar return because of their configuration.
Bleed air is air taken from the compressor section of a gas turbine engine, whether a main propulsion engine of the aircraft or a so-called APU or auxiliary power unit. A penalty paid for the use of bleed air is a reduction in operating efficiency of the engine from which the air is bled.
Many of these systems utilize aircraft fuel as a coolant prior to its combustion in an engine. The aircraft fuel cannot be heated to such a degree that it begins to xe2x80x9ccokexe2x80x9d and consequently, excess fuel is circulated to the components that it is to cool and that fuel not required by the engine is recirculated to the fuel reservoir. Not infrequently, this fuel, particularly in military usages, may be returned to another, larger storage reservoir, from which fuel is withdrawn to be put to uses other than that of driving the main propulsion engines of the aircraft. Because of that possibility, desirable additives for aircraft operation cannot be utilized in the fuel. For example, it is desirable to use additives that raise the temperature of the fuel at which coking begins to occur and the presence of such additives may not be desirable for all uses to which the fuel is put and can be expensive.
The present invention is directed to overcoming one or more of the above problems.
It is the principal object of the invention to provide a new and improved, integrated, thermal management and environmental cooling system. An exemplary embodiment of the invention contains a number of facets which, in a highly preferred embodiment, are all used together. However, in some instances, components giving but a single advantage may be employed exclusively without resort to the others or in such combinations as to achieve those of the advantages specifically desired.
According to one aspect of the invention, the system includes a fuel reservoir with a pump pumping fuel from the reservoir to a first heat load. A check valve is located downstream of the first heat load and upstream of a second heat load. The fuel, after being passed through the heat loads, is further heated by engine bleed air with part being diverted to the main propulsion engine for combustion therein and the remainder being recirculated through a heat exchanger cooled by fan air from an early stage of the engine and returned to the fuel line downstream of the check valve. Consequently, recirculation is not through the fuel tank and the problems associated with the return of recirculated fuel to the fuel reservoir or tank are avoided.
According to another aspect of the invention, the thermal management and coolant system avoids the use of ram air altogether by employing, when required, engine fan air from the fan duct of a turbo fan engine and engine bleed air from the compressor of the main engine core as the air utilized throughout the system in exclusion to ram air entirely.
According to the invention and another facet thereof, heat exchangers for cooling the air used as a working fluid in the system are located in the bypass or fan air duct of the engine to reduce the fuselage volume and to increase efficiency by rejecting heat to the fan or bypass air passing through the engine.
In another facet of the invention, fan air utilized in a heat exchanger to cool fuel that is being recirculated to the heat loads is discharged to the engine bay to provide positive bay ventilation and eliminate the need for separate engine bay ventilation circuits.
In still another aspect of the invention, the system employs a turbo machine having at least one turbine stage. Engine fan air is expanded in the one turbine stage, and thereby cooled while undergoing expansion, before being discharged to an early part of a thermal management network. The one turbine stage thereby lowers the temperature of the air being utilized as the sink for the system.
Additionally, the system of the invention, because it does not require ram air, may be located extremely close to the main propulsion engine to minimize ducting.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.